Diffs that have no real conflict (direct or indirect) and only some
pseudo-conflicts (but also non-conflicting refining diffs) only appear
in the side group.
Also add javadoc to describe the expected behaviour of the group
provider 'by side' and some unit tests for predicates.
Change-Id: I3d02172b1c77199ea0904459b196289b19db35d6
Signed-off-by: Laurent Delaigue <laurent.delaigue@obeo.fr>